Characterization of a human H9N2 influenza virus isolated in Hong Kong

Vaccine. 2001 Oct 12;20(1-2):125-33. doi: 10.1016/s0264-410x(01)00279-1.


Two H9N2 viruses were isolated, for the first time, from humans in Hong Kong in 1999. Isolation of influenza viruses with a novel subtype of the hemagglutinin (HA) drew attention of health care authorities worldwide from the view of pandemic preparedness. Sequence analysis of the HA genes reveals that HA of A/Hong Kong/1073/99 (H9N2) is most closely related to that of A/quail/HK/G1/97 (H9N2) that contains the internal genes similar to those of Hong Kong/97 (H5N1) viruses. Phylogenetic and antigenic analyses demonstrated the diversity among H9 HA. A/Hong Kong/1073/99 was shown to cause a respiratory infection in Syrian hamsters, suggesting that the virus can replicate efficiently in mammalian hosts. We developed a whole virion test vaccine with a formalin-inactivated egg-grown HK1073. Intraperitoneal administration of the vaccine twice to hamsters conferred a complete protection against challenge infection by the MDCK cell-grown homologous virus. Receptor specificity of HK1073 appeared different from that of other avian influenza viruses of H9 subtype which recognize preferentially alpha-2,3 linked sialic acid. Hemagglutination of HK1073 with guinea pig erythrocytes was inhibited by both alpha-2,3 and alpha-2,6 linked sialic acid containing polymers. These data suggested that HK1073 had acquired a broader host range, including humans. Together with data so far available, the present study suggested that isolation of the H9 influenza viruses from humans requires precaution against the emergence of a novel human influenza.

Publication types

  • Comparative Study

MeSH terms

  • Animals
  • Antigens, Viral / immunology
  • Asia
  • Cattle
  • Cells, Cultured
  • Chick Embryo
  • Child
  • Cricetinae
  • Dogs
  • Europe
  • Female
  • Glycoconjugates / pharmacology
  • Guinea Pigs
  • Hemagglutination Tests
  • Hemagglutination, Viral
  • Hemagglutinin Glycoproteins, Influenza Virus / genetics
  • Hemagglutinin Glycoproteins, Influenza Virus / physiology
  • Hong Kong
  • Horses
  • Humans
  • Influenza A Virus, H9N2 Subtype*
  • Influenza A virus / classification
  • Influenza A virus / genetics
  • Influenza A virus / immunology
  • Influenza A virus / isolation & purification*
  • Influenza A virus / physiology
  • Influenza Vaccines / immunology
  • Influenza, Human / prevention & control
  • Influenza, Human / veterinary
  • Influenza, Human / virology*
  • Lung / virology
  • Male
  • Mesocricetus
  • N-Acetylneuraminic Acid / metabolism
  • North America
  • Phylogeny
  • Poultry / virology
  • Poultry Diseases / virology
  • Receptors, Virus / metabolism
  • Sheep
  • Species Specificity
  • Swine
  • Swine Diseases / virology
  • Vaccination
  • Vaccines, Inactivated
  • Virion / immunology
  • Virus Cultivation


  • Antigens, Viral
  • Glycoconjugates
  • Hemagglutinin Glycoproteins, Influenza Virus
  • Influenza Vaccines
  • Receptors, Virus
  • Vaccines, Inactivated
  • N-Acetylneuraminic Acid